1. Clinical Overview
Methylphenidate is a central nervous system (CNS) stimulant of the phenethylamine and piperidine classes. It is a first-line pharmacological agent for the treatment of Attention Deficit Hyperactivity Disorder (ADHD) and is also indicated for narcolepsy. It primarily acts by blocking the reuptake of dopamine and norepinephrine in the presynaptic neuron, increasing their concentration in the synaptic cleft. In India, it is a strictly regulated Schedule X drug under the Drugs and Cosmetics Act, 1940, requiring a special prescription.
| Onset | Duration | Bioavailability |
|---|---|---|
| Approximately 1 to 2 hours for immediate-release formulations. | 3 to 6 hours for immediate-release formulations. | Approximately 30% for oral immediate-release tablets due to significant first-pass metabolism. |
2. Mechanism of Action
Methylphenidate is a potent blocker of the dopamine transporter (DAT) and norepinephrine transporter (NET). It binds to these transporters on the presynaptic neuronal membrane, inhibiting the reuptake of dopamine and norepinephrine from the synaptic cleft back into the presynaptic neuron. This leads to a significant increase in the extracellular concentrations of these neurotransmitters in key brain regions, particularly the prefrontal cortex and striatum.
3. Indications & Uses
- Attention Deficit Hyperactivity Disorder (ADHD) in children (aged 6 years and above), adolescents, and adults
- Narcolepsy
4. Dosage & Administration
Adult Dosage: ADHD: Start with 5mg once or twice daily (e.g., morning and noon). Titrate gradually by 5-10mg increments weekly based on response and tolerability. Typical effective dose range: 20-30mg/day in 2-3 divided doses. Maximum: 60mg/day. Narcolepsy: 20-30mg/day in divided doses.
Administration: Administer orally, with or without food (food may delay absorption). Tablets should be swallowed whole with water. Doses are typically given in the morning and early afternoon to avoid insomnia. The last dose should not be taken after 4-6 PM. Do not crush or chew unless specifically instructed (some brands may have different formulations).
5. Side Effects
Common side effects may include:
- Decreased appetite, weight loss
- Insomnia, nervousness
- Headache, dizziness
- Nausea, abdominal pain
- Dry mouth
- Tachycardia, palpitations
- Increased blood pressure
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) - e.g., Phenelzine, Selegiline | Risk of hypertensive crisis, hyperpyrexia, serotonin syndrome. Potentially fatal. | Contraindicated |
| Anticoagulants (e.g., Warfarin) | Methylphenidate may inhibit metabolism of warfarin, increasing INR and bleeding risk. | Major |
| Anticonvulsants (e.g., Phenobarbital, Phenytoin, Primidone) | Methylphenidate may increase levels of these drugs, leading to toxicity. | Major |
| Tricyclic Antidepressants (TCAs - e.g., Imipramine, Desipramine) | Mutual inhibition of metabolism; increased levels of both drugs. Increased risk of cardiovascular effects. | Major |
| Pressor Agents (e.g., Dopamine, Epinephrine) | Additive pressor effects, leading to severe hypertension. | Major |
| Clonidine | Possible serious adverse events including sudden death reported (controversial, use with extreme caution). | Major |
| Alcohol | May alter the absorption profile of methylphenidate. CNS depression may be masked. Increases risk of cardiovascular side effects. | Major |
7. Patient Counselling
- DO take the medication exactly as prescribed by your doctor.
- DO inform all your doctors and dentists that you are taking this medicine.
- DO monitor your weight regularly, especially in children.
- DO NOT stop taking the medicine suddenly without consulting your doctor.
- DO NOT crush, chew, or break the tablet unless advised.
- DO NOT share this medicine with anyone else; it is a controlled substance.
- DO NOT take a double dose to make up for a missed one.
8. Toxicology & Storage
Overdose: Symptoms are primarily extensions of its pharmacologic effects and include: Vomiting, agitation, tremors, hyperreflexia, muscle twitching, convulsions (may be followed by coma), Euphoria, confusion, hallucinations, delirium, Sweating, flushing, headache, hyperpyrexia, Tachycardia, palpitations, cardiac arrhythmias, hypertension (may be followed by hypotension and circulatory collapse.
Storage: Store at room temperature (15-25°C), protected from light and moisture. Keep in the original container, tightly closed. Keep out of reach of children and in a secure place to prevent misuse, abuse, or theft. Do not flush unused medication. Dispose of as per pharmacist's advice or take-back programs.